A generator is axially coupled to a prime mover that converts a natural energy, such as wind power, water power and nuclear power, into a mechanical energy so as to convert the mechanical energy of the prime mover into an electric energy. The generator is configured in such a manner that rotating magnetic fluxes of a rotator, which is axially coupled to the prime mover, are linked to a stator, which is fixed to the outer circumferential surface of the rotator with a gap, thereby generating an electromotive force.
A small generator is configured in such a manner that permanent magnets are mounted on a rotator in place of a field winding to link rotating magnetic fluxes to an armature winding wound on a stator. Conventionally, N-pole and S-pole permanent magnets are alternately arranged along the outer circumferential surface of the rotator, so that processes of linking the armature winding to an N-pole and then to an S-pole may be repeated to generate an electromotive force close to a sine wave.
However, in a conventional generator, the N-poles form boundaries with the S-poles along an axial direction, and a space exists at each of the boundary parts, which causes the magnetic fluxes linked between the N-poles and S-poles to be abruptly fluctuated. As a result, an electromotive force induced thereby is distorted rather than being formed in a sine wave form. To this end, the induced electromotive force, which is not formed in a sine wave form, contains a lot of harmonic wave components, and causes a problem in that the harmonic wave components contained in the electromotive force result in copper loss in the armature winding, thereby decreasing electricity generating efficiency and adversely affecting a load device which is supplied with the induced electromotive force. That is, a part of energy, which should be converted into the electromotive force with a desired sine wave form, is converted into harmonic components that merely decrease electricity generating efficiency and have a detrimental effect.
In addition, when the coil of the armature winding passes while being opposed to a magnetic pole (N-pole or S-pole), it is impossible to generate an electromotive force with a sine wave form since linkage to the coil is made with uniform fluxes throughout the passage.
That is, when a flux distribution by magnetic poles in the conventional generator is shown along a cylindrical surface, the distribution is close to a square wave where magnetic fluxes are abruptly fluctuated at empty spaces between magnetic poles. Therefore, there is a problem in that the induced electromotive force cannot be formed in a sine wave form.
In order to solve this problem, the prior art obtains an electromotive force close to a sine wave form by distributing a plurality of windings around the stator and connecting the windings in serial. However, this winding method is too complicated to be applied to a small generator.
Meanwhile, since an induced electromotive force is fluctuated depending on the revolution speed of a rotator, the prior art employs a method for keeping the revolution speed of a prime mover axially coupled to the rotator constant in order to generate a predetermined electromotive force.
However, providing a control means for keeping the revolution speed of the prime mover is difficult to employ since providing such a control means in a small generator, which uses wind power or water power, is uneconomic in view of securing the costs and spaces for installing the generator. As such, the control means has not been employed, and an arrangement configured to release the axial coupling with the prime mover has been used in place of the control means in order to prevent excessive power generating. However, this makes it difficult to utilize wind power or water power properly, thereby decreasing generating efficiency.